1. Field of the Invention
The present invention relates to a method for improving acid tolerance and propionic acid productivity of Propionibacterium acidipropionici, and more particularly relates to a method of improving acid tolerance and propionic acid productivity of P. acidipropionici by adding arginine and aspartic acid during the cultivation of P. acidipropionici. 
2. Description of the Related Art
The sustainable development of our society is severely hindered by energy shortages and environmental pollution. Using renewable biomass resources as raw materials for large-scale production of chemical products, medicine, food and agricultural materials is considered to be a promising way to resolve the current energy shortage and environmental crisis.
Propionic acid (PA) is an important mold inhibitor, and its calcium, sodium and potassium salts are widely used as food and feed preservatives. PA can also be used as a chemical intermediate for the synthesis of cellulose fibers, herbicides, perfumes, and pharmaceuticals. Currently, PA is mainly produced by petrochemical approaches. With the increasing concerns over environmental pollution and energy shortages, the microbial production of PA by propionibacteria receives ongoing interest and extensive studies have been done to improve PA yield. Microbial PA production is a typical product-inhibited process, and the accumulation of PA severely inhibits both cell growth and PA synthesis. To resolve this problem, NaOH or Ca(OH)2 was added to maintain the pH at a stable level, which unfortunately will increase the osmotic pressure of fermentation broth and the costs of downstream extraction. Therefore, improving the acid tolerance of PA-producing microbes is an effective approach to increase microbial PA production. The present invention satisfies this need and provides other benefits.